Ultrasonic impingement plate atomizer apparatus

ABSTRACT

An impingement plate atomizer apparatus includes a longitudinal member having an upper surface sized and shaped to receive a liquid cryogen thereon, a lower surface opposite to the upper surface, and at least one hole extending through the longitudinal member; and an ultrasonic transducer in contact with the longitudinal member for providing ultrasonic energy thereto for atomizing the liquid cryogen at the upper surface into a cryogen fog.

BACKGROUND

The present embodiments relate to freezer apparatus used to cause heat transfer to objects, such as for example food products, by the application of a cryogen to same.

In a cryogenic food freezing system, nitrogen liquid, for example, is sprayed into a freezing chamber to provide refrigeration for the system process. It is desirable to spray the liquid nitrogen onto the warm surface of the incoming food product so that a phase change (heat of vaporization) occurs on the surface of the food product. This evaporative cooling effect creates extremely high heat transfer coefficients. Until now, it has been very difficult if not impossible to direct a high portion of the liquid spray onto the food product, as the spray is injected through nozzles that are positioned in a freezing chamber above a belt upon which the products travel for processing. Although a portion of the liquid nitrogen is deposited onto the surface of the product, another portion of the nitrogen travels to and through the belt without contacting the product. This results in an inefficient use of the liquid cryogen.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present inventive embodiments, reference may be had to the following drawing figures taken in conjunction with the description of the embodiments, of which:

FIG. 1 shows an ultrasonic impingement plate atomizer apparatus embodiment of the present invention; and

FIG. 2 shows an enlarged portion of the embodiment in FIG. 1.

DETAILED DESCRIPTION OF THE INVENTION

As discussed below with respect to the present invention, when liquid nitrogen (N₂) is atomized, the atomized droplets provide for a faster or higher heat transfer rate when the nitrogen spray is deposited onto the food product, thereby maximizing overall evaporative heat transfer at the product and use of the nitrogen. This is because the atomization of liquid nitrogen produces very small size droplets. As a result of the small droplet size, the volume of liquid nitrogen, now in an atomized state, has a very high surface area. These small droplets with high surface area produce extremely high evaporative heat transfer rates when introduced for direct contact with a warm product such as for example a food product.

The liquid nitrogen is disposed on an impingement plate and then atomized by an ultrasonic transducer coacting with the plate to therefore effectively replace cryogen nozzles in a freezing process.

Referring to FIGS. 1 and 2, the ultrasonic impingement plate atomizer apparatus shown generally at 10 includes an impingement plate 12 positioned above a conveyor 11 for transporting a food product 14 to be frozen. The plate 12 may be constructed of stainless steel, aluminum, plastics including UHMW (ultra high weight molecular) or Teflon and holds or retains a quantity of liquid cryogen, such as for example liquid nitrogen 16. This is accomplished by the plate 12 having an upper surface 18 and an edge 20 extending upward therefrom to retain a select amount of the liquid nitrogen 16 on the upper surface 18. As shown in FIG. 1, the edge 20 extends along an outer perimeter or periphery of the plate 12, but can also be constructed to extend along the plate at another area thereof where necessary to retain the liquid nitrogen.

The plate 12 is formed with at least one or a plurality of holes 22 or apertures therethrough, each one of the holes 22 having an edge 24 turned upward away from the conveyor belt 11 to facilitate the flow of gas as described below. The holes 22 can be arranged in a myriad of different patterns at the plate 12. The raised or elevated surface area 24 extends around each one of the holes 22 to prevent the liquid nitrogen 16 from pouring or seeping through the holes 22 before the nitrogen has been atomized. The raised surface area 24 functions as a dam and can be formed on the upper surface 18 by for example either pressing the plate 12 to have the upper surface 18 between the raised surface areas 24 in relief as compared to the areas 24 with same extending above the upper surface 18 as shown in FIG. 2, or by providing a wall of material to extend upward around the edges 24 of the holes 22. The raised surface area 24 may be formed integral with the plate 12. Although the holes 22 are shown having a circular shape, other shapes for the holes may be used. The liquid nitrogen 16 may be provided to the upper surface 18 from a pipe 19 having a first end connected to a cryogen source (not shown) and a second outlet end 23 proximate the upper surface for providing the liquid cryogen to the upper surface 18 to maintain a constant level of nitrogen at said surface of the plate.

At least one ultrasonic transducer 26 is mounted to the upper surface 18 of the impingement plate 12. The at least one ultrasonic transducer 26 may also be mounted (as at 26A) to another area of the impingement plate 12, such as a lower surface 34 of the plate depending upon the amount of space and operational environment available in which to use the apparatus 10. The ultrasonic transducer 26 provides high frequency vibration to the impingement plate 12 as represented by arrow “V”. The transducers 26,26A can be provided at both the upper surface 18 and/or the lower surface 34 of the impingement plate 12 to provide ultrasonic energy to the plate.

The high frequency vibration “V” will cause the liquid nitrogen 16 disposed on the plate 12 to break-up into small atomized droplets 28. High velocity gas jets 30 are created by a flow of atomized nitrogen gas 28 through the holes 22 of the impingement plate 12 by internal fans (not shown). The nitrogen droplets 28 are entrained in the gas jets 30 and forced through the holes 22.

Alternatively, and referring to FIG. 2, the edge 24 can be turned downward as shown by the broken line 25 toward the food product 14 to facilitate the flow of the gas jets 30 through the holes 22. If the edge 25 is used, a raised or elevated surface area 27 would extend around each one of the holes 22 to prevent the liquid nitrogen 16 from pouring or seeping through the holes 22 before the nitrogen has been atomized. The raised surface area 27 functions as a dam and can be formed on the upper surface 18 by for example pressing the plate 12 to have the upper surface 18 between the raised surface areas 27 in relief. The raised surface area 27 may also be formed integral with the plate 12.

Although the holes 22 are shown having a circular shape, other shapes for the holes may be used. A nitrogen injection system (not shown) may also be used to provide a constant level of nitrogen at the surface 18 of the plate 12.

The droplets 28 are discharged from the holes 22 to be deposited on the product 14. The food product 14 is positioned closest to the discharge of the holes 22 by being transported upon the conveyor 11, such as a belt, as shown in FIG. 2. The ultrasonic energy transferred to the impingement plate 12 creates the droplets 28 to be of such a small size that the entrainment of the droplets 28 in the gas jets 30 provides for an atomized nitrogen fog 32 to be deposited upon the food product transported on the conveyor 11. The fog 32 is very effective for covering or blanketing the exposed surface of the food product 14 as it is deposited thereon, instead of being deposited on the conveyor 11 or passing through the conveyor.

The embodiment 10 can be constructed and arranged in a new freezer, or retrofit to an existing freezer.

It will be understood that the embodiments described herein are merely exemplary, and that one skilled in the art may make variations and modifications without departing from the spirit and scope of the invention. All such variations and modifications are intended to be included within the scope of the invention as described and claimed herein. Further, all embodiments disclosed are not necessarily in the alternative, as various embodiments of the invention may be combined to provide the desired result. 

What is claimed is:
 1. An impingement plate atomizer apparatus, comprising: a longitudinal member having an upper surface sized and shaped to receive a liquid cryogen thereon, a lower surface opposite to the upper surface, and at least one hole extending through the longitudinal member; and an ultrasonic transducer in contact with the longitudinal member for providing ultrasonic energy thereto for atomizing the liquid cryogen at the upper surface into a cryogen fog.
 2. The apparatus of claim 1, wherein the longitudinal member further comprises: an elevated edge extending from the upper surface for retaining the liquid cryogen at the upper surface.
 3. The apparatus of claim 1, wherein the longitudinal member further comprises a raised surface area extending upward from the upper surface and surrounding the at least one hole to prevent the liquid cryogen from passing through the at least one hole.
 4. The apparatus of claim 1, wherein the longitudinal member further comprises a raised surface area extending downward from the upper surface and surrounding the at least one hole, and a lip extending upward from the upper surface of the plate and around the at least one hole.
 5. The apparatus of claim 1, wherein the ultrasonic transducer is in contact with the upper surface of the longitudinal member.
 6. The apparatus of claim 5, further comprising another ultrasonic transducer in contact with the lower surface of the longitudinal member.
 7. The apparatus of claim 1, wherein the liquid cryogen comprises liquid nitrogen.
 8. The apparatus of claim 1, further comprising a conveyor disposed for movement beneath the lower surface of the longitudinal member for transporting a product beneath the at least one hole for contact with the cryogen fog.
 9. The apparatus of claim 1, further comprising a pipe having a first end connected to a source of the liquid cryogen, and a second end having an outlet proximate the upper surface of the longitudinal member for providing the liquid cryogen to the upper surface.
 10. The apparatus of claim 1, wherein the product comprises a food product.
 11. The apparatus of claim 1, wherein the longitudinal member comprises a plate.
 12. The apparatus of claim 1, wherein the longitudinal member is constructed from a material selected from the group consisting of stainless steel, aluminum, and plastic.
 13. A method of providing a cryogen fog, comprising: providing liquid cryogen to a longitudinal member; providing ultrasonic energy to the longitudinal member for atomizing the liquid cryogen into cryogen droplets; and entraining the cryogen droplets in a cryogen gas flow for providing a cryogen fog.
 14. The method of claim 13, further comprising retaining the liquid cryogen at a surface of the longitudinal member.
 15. The method of claim 13, further comprising providing the cryogen fog to a product to reduce a temperature of said product.
 16. The method of claim 13, wherein the liquid cryogen comprises liquid nitrogen. 